Open RAN Capacity Calculator
Dimension O-RAN fronthaul bandwidth (eCPRI), DU count, and CU-UP capacity for 5G NR deployments. Supports 2T2R to 64T64R antenna configurations and Block Floating Point (BFP) compression per O-RAN WG4.
RU ──[eCPRI FH]──▶ DU ──[midhaul]──▶ CU-UP ──[backhaul]──▶ UPF (5GC)
(O-RAN 7-2x split) CU-CP ──[backhaul]──▶ AMF (5GC)
7-2x = low-PHY stays in RU; high-PHY, MAC/RLC in DU; PDCP/RRC/SDAP in CU
Site Parameters
Total macro/micro sites in the deployment
Radio Parameters
O-RAN WG4 CUS spec — BFP-9 is widely deployed
Node Dimensioning
Vendor-dependent — typically 6–18 cells/DU
User-plane throughput per CU-UP instance
Busy-hour U-plane throughput design target
1.0 = none, 1.3 = N+1/3 spare, 2.0 = full redundancy
Total RUs
50 sites × 3 sectors
Fronthaul BW per RU
eCPRI, BFP-9
Total fronthaul capacity
150 RUs × 74.3 Gbps
Fronthaul port per RU
25GE SFP28 typically sufficient
DUs required
incl. 1.3× redundancy
CU-UPs required
incl. 1.3× redundancy
Total U-plane throughput
150 RUs × 500 Mbps
About O-RAN 7-2x Split
In the O-RAN 7-2x functional split, the RU handles RF, analog beamforming, and low-PHY (FFT/iFFT, PRACH extraction). The DU handles high-PHY (channel estimation, equalization), MAC, and RLC. The CU is split into CU-CP (RRC, PDCP-C) and CU-UP (PDCP-U, SDAP). Fronthaul uses eCPRI over Ethernet, requiring low-latency transport (<100 µs one-way) and precise timing (IEEE 1588v2/PTP).
Fronthaul formula: BW = 2 × Fs × bits × ports × 1.05 overhead. Ref: O-RAN WG4 CUS specification.
eCPRI Fronthaul Reference
Fronthaul bandwidth formula (O-RAN WG4)
BW = 2 × Fs × bits × antenna_ports × (1 + overhead%)
2 = I and Q components | overhead ≈ 5% (eCPRI protocol) | result in Gbps
Sampling rate by NR channel bandwidth
| NR BW | Numerology (μ=1) | Fs (MSPS) |
|---|---|---|
| 10 MHz | SCS 30 kHz | 15.36 |
| 20 MHz | SCS 30 kHz | 30.72 |
| 40 MHz | SCS 30 kHz | 61.44 |
| 50 MHz | SCS 30 kHz | 61.44 |
| 80 MHz | SCS 30 kHz | 122.88 |
| 100 MHz | SCS 30 kHz | 122.88 |
eCPRI compression options
| Mode | Bits/sample | BW reduction | Notes |
|---|---|---|---|
| None (16-bit) | 16 | Baseline | Uncompressed IQ — very high BW for massive MIMO |
| BFP-14 | 14 | ~12% | Block floating point, 14-bit mantissa |
| BFP-9 | 9 | ~44% | Widely deployed; recommended for 32T32R / 64T64R |
| Mod Comp (~6-bit) | ~6 | ~62% | Modulation-dependent; highest compression, vendor-specific |
Reference: O-RAN.WG4.CUS.0 — Control, User and Synchronisation Plane Specification.
Frequently Asked Questions
What is Open RAN (O-RAN)?▾
Open RAN (O-RAN) is a disaggregated, open-interface radio access network architecture defined by the O-RAN Alliance. The traditional monolithic base station is split into three logical units: the RU (Radio Unit) which handles RF and low-level PHY processing, the DU (Distributed Unit) which handles higher PHY and MAC/RLC, and the CU (Centralised Unit) which handles PDCP, RRC, and SDAP. The interfaces between them — eCPRI/fronthaul (RU–DU), midhaul (DU–CU), and backhaul (CU–Core) — are open and standardised, enabling multi-vendor deployments.
What is eCPRI and how is fronthaul bandwidth calculated?▾
eCPRI (enhanced Common Public Radio Interface) is the transport protocol between the RU and DU in O-RAN 7-2x split deployments. The fronthaul bandwidth depends on the NR channel bandwidth, number of antenna ports, IQ sample bit width, and whether compression is applied. The formula is: BW = 2 × Fs × bits × antenna_ports × (1 + OH%), where Fs is the sampling rate (e.g. 122.88 MSPS for 100 MHz NR) and OH is protocol overhead (~5%). For 64T64R at 100 MHz without compression, this exceeds 250 Gbps per RU — making IQ compression (BFP-9 or modulation compression) essential.
What is BFP compression in O-RAN?▾
Block Floating Point (BFP) compression reduces the per-sample bit width from 16 bits to 9 or 14 bits by sharing a floating-point exponent across a block of IQ samples. BFP-9 (9-bit mantissa) is widely supported and reduces fronthaul bandwidth by ~44% compared to uncompressed 16-bit IQ. Modulation-dependent compression can reduce it further. The O-RAN WG4 fronthaul compression specification (O-RAN.WG4.CUS.0) defines the signalling for negotiating compression parameters between RU and DU.
How many DUs and CU-UPs does an O-RAN deployment need?▾
The number of DUs depends on how many cells (RUs) each DU can serve — typically 6–18 cells per DU depending on vendor and configuration. Each DU handles the Layer 1 / Layer 2 processing for its attached RUs. CU-UP nodes handle user-plane packet processing (GTP-U tunnelling, QoS) and are dimensioned by throughput (Gbps). CU-CP nodes handle control-plane sessions (RRC, PDCP-C) and are dimensioned by the number of connected UEs. Redundancy (typically N+1 or N+2) must be factored into all node counts.